This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
Home Products Support Community News


Re: [Xen-devel] CPU enumeration in Xen

To: "Daniel P. Berrange" <berrange@xxxxxxxxxx>
Subject: Re: [Xen-devel] CPU enumeration in Xen
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Wed, 22 Aug 2007 14:53:08 +0100
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, Dominik Klein <dk@xxxxxxxxxxxxxxxx>
Delivery-date: Wed, 22 Aug 2007 06:53:59 -0700
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <20070822134855.GB18061@xxxxxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: Acfkw8UbA/JH0lC3Edyp4wAX8io7RQ==
Thread-topic: [Xen-devel] CPU enumeration in Xen
User-agent: Microsoft-Entourage/
On 22/8/07 14:48, "Daniel P. Berrange" <berrange@xxxxxxxxxx> wrote:

>> To my knowledge the enumeration order is determined by the order we find
>> CPUs in the BIOS tables, and can hence vary across different systems, and
>> even across BIOS upgrades.
> The HV may enumerate CPUs in the same way as Linux baremetal, but Dom0 sees
> VCPUs not physical CPUs. So /proc/cpuinfo in Dom0 will bear little resemblance
> to the same file on a bare metal machine. You'd need to compare the HV's view
> of physical CPUs to the Linux bare metal view, which isn't something you can
> do  by merely comparing /proc/cpuinfo AFAICT.

Oh yes, I missed this stunningly obvious point. :-)

If you want to tie dom0 VCPUs 1:1 with physical CPUs then you can put
dom0_vcpus_pin on your Xen command line.

To see how Xen enumerates the CPUs: look at 'xm dmesg', or look at Xen boot
output, to see APIC IDs of processors as they are booted.

 -- Keir

Xen-devel mailing list